Sonoma County: Dry year water supply update

SONOMA WATER E-NEWS – April 2021 Special Edition

Water Supply Reservoirs Reach Historic Lows

The Russian River basin is experiencing a second consecutive year of severely below-average rainfall. As a result, water supply levels at Lake Mendocino and Lake Sonoma are at historic lows. While state officials have yet to officially declare a drought, hydrologic conditions are more severe than the drought years of 2013 through 2014.

Last week the State Water Resources Control Board (SWRCB) issued early warning notices to approximately 40,000 water rights holders statewide, urging them to plan for potential shortages by reducing water use and adopting practical conservation measures. These notices indicate the seriousness of the situation for water users throughout the Russian River watershed. We anticipate voluntary water conservation measures to be adopted by our Water Contractors and the potential for mandatory measures as well.

Sonoma Water is very concerned about water levels in Lake Mendocino and Lake Sonoma. Lake Mendocino is at 46% of the target supply curve and Lake Sonoma is at 63% of water supply capacity. Both reservoirs are at the lowest storage level for this time of year since they filled. Hydrologic modelling by Sonoma Water engineering staff indicates that without timely measures to reduce diversions from the Russian River, Lake Mendocino could reach levels too low to support releases for water supply and fish migration by fall of 2021.

What We Are Doing
Since the summer of 2020, Sonoma Water has been working closely with staff at the SWRCB to develop a plan to manage reservoir releases, minimum instream flows and diversions by Russian River water users to prevent both Lake Mendocino and Lake Sonoma from reaching severely low storage levels. Currently, Lake Mendocino is being operated in accordance with a second consecutive Temporary Urgency Change Order issued to Sonoma Water by the SWRCB that reduces minimum in-stream flows in the upper Russian River (above confluence of Dry Creek) to preserve water supply storage in Lake Mendocino. An option under consideration is the filing of a new Temporary Urgency Change (TUC) Petition. This would replace the current TUC Order that expires July 28, 2021 and could include reduced minimum in-stream flows in the lower river (below Dry Creek) and a proposal for Sonoma Water to voluntarily reduce diversions from the Russian River.

The TUC Petition Sonoma Water filed in January of 2021 acknowledged that it might request changes to lower Russian River flows if conditions worsened, which they have. Sonoma Water is working with the SWRCB and our Water Contractors to determine what would be requested in a new TUC Petition. Modelling indicates that if Sonoma Water and Russian River water users take no action, storage in both Lake Mendocino and Lake Sonoma would reach historic lows by the fall of this year. In addition to coordinating reservoir releases, we will also closely monitor upper Russian River stream gages and track stream flow losses.

Proposed flow changes and diversion reductions by Sonoma Water alone will not be enough to address the water supply challenges the region faces. It will require a concerted and coordinated effort by all users to reduce water use from the Russian River. Sonoma Water will work with water users throughout the entire watershed – urban, agricultural, recreational – to reduce water use and diversions and to share in the response to meet the challenge of reduced reservoir releases and stream flows.

The Sonoma Marin Saving Water Partnership (Partnership) has launched a Winter-Spring Saving Water Campaign with all its members. This campaign includes print, digital and radio advertising to encourage water saving practices, with an emphasis on outdoor water use reductions. The Partnership is collaborating with the upper Russian River water managers on the water-saving campaign and is preparing to broaden its water conservation campaign with increased advertising, public events and targeted outreach as the summer months approach.

Sonoma Water will continue to closely monitor water supply conditions locally and work with SWRCB staff, Russian River stakeholders, and Water Contractors to navigate the situation and maintain communications with its Board of Directors, customers, and the greater community.

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